While a tool is moved over the surface of a part by a CNC machine, the tool is, in general, performing some kind of treating on the part. The result of the treatment is dependent on treating the surface under optimal conditions, like treating the surface under predetermined angles and in preferred directions associated with the structure of the material. To achieve good results for treating, a preferred path for moving the tool during treating is defined based on a model of the shape of the surface as it is expected to be formed based on theoretical considerations.
However, if the part has undergone steps of treatment before, some wear may have occurred which has the consequence that the actual shape of the part to be processed is somewhat different from its theoretical shape. So, following the preferred path for further treating the surface leads to working on the surface in positions, directions and/or under angles which differ from the ones planned for optimal treatment. Particularly near ranges with large curvatures, like edges, the differences between the planned and the actual working conditions for the tool may be considerable.
To obtain a better adaptation of the treatment to the actual shape of the surface of the part, the system disclosed by WO 2007/016919 teaches determining optimal paths for moving the tool, based on geometry data of the desired 3D surface and of the tool. The disclosed system may be combined with a mechanical or non-contact measurement process (like LASER measurement) to obtain intelligent and autonomous processing of the surface. 3D-shapes of the surface, tolerances as well as roughness and resistance of the surface are taken from the drawing program and performed by the disclosed system.
Moreover, the article “Hämmern bis zum Glanz”, werkzeug & formenbau, March 2007, page 36, mentions a method of hammering a surface where, after having exchanged a previous tool against a hammer tool and keeping the part in its mounting for further treatment, the CAM-system can apply a correction to the preferred path of the tool, based on the existing CAM program.
However, in both cases, the tool is moved along a path, derived from existing geometry data or an existing CAM program, before treating the surface. The CNC machine according to the prior art is not provided with a possibility of changing the direction of moving the tool over the surface to preserve optimal working conditions, in particular, working under optimal angles and/or in optimal directions, if differences between the theoretical and the actual shape of the surface are detected during treatment. So, in the case of differences between theoretical and actual shape, e.g. caused by wear of a part during former production steps, processing the surface is performed, according to the prior art, along a predetermined path which is optimized based on predetermined conditions, but is not adapted to the actual shape of the surface. Particularly, WO2007/016919 does not provide any further explanation of what is measured and how the measurement is accomplished. Moreover, WO2007/016919 does not specify in which way the additional measurement process may be employed to obtain better treatment results.